i checked the tapets on and they were all within spec so i decided to remove the cylinders and barrels to inspect them.

it turns out the previous owner has installed 1000cc barrels and pistons without any modifications. to make it worse he has filed down the tops of the pistons to prevent them hitting the heads.

it gets worse still, the pistons aren;t even the same. one has circlips which you take out using cirlclip pliers and the other has the ciclips you pry out with a screwdriver. the tops od the pistons also have a different shape.

i have decided to put the egine back to stock by buying some second hand 800cc pistons and barrels and then reset the carbs back to stock settings.

does anyone have any tips for checking the valve seats will i have the head off?

oil consumption was low and the bike blows no white smoke so i am guessing the valve guides are in good repair.

a friend suggested turning the heads upside down and filling them with petrol to see if they are sealing. if petrol leaks through them i need to regrind the seats. does this sound like a good tip?

while i am in there i am going to replace the rockers as they are showing signs of pitting, does any one know what year models have interchangable rockers with an 83 r80g/s to make buying a second hand set of rockers easier?

It might be cheaper to fit a pair of 1000 cc pistons from Siebenrock. Motobins sell them.
also fit new float valves as the wear you mentioned is not good. At the same time replace the needles and needle jets. My 1985 r80rt went from 280km per tankfull to over 320km per tankful with just the needles/needle jets. the siebenrock pistons will work without modifying heads or carburetters.

I prefer your idea of returning to stock better, unless you need the extra power the Siebenrock kit should produce and are aware of the trade off's. This kit increases compression quite a bit, and is not recommended for fuel of less then 95 octane. Not a problem in most countries, but not always obtainable in much of the world so this is a limitation for adventure touring.

a brand new set (or good used) of 800cc pistons and barrels from Motobins or another good BMW supplier is not a huge expense, and going back to stock will better enable you to sort out the issues with the bike.

The 800cc engine is very smooth and should produce adequate power and good economy if tuned properly. It really depends on your priorities, but if you are wanting to use the bike for long distance travel then be sure you are aware of the potential trade off's with each modification.

Good luck and let us know what you did and how it worked.

I owned a R80 for about 40 000km. Consumption should be at least 17-22 km /litre. All I would like to add is to put an inline fuel filter each side above the carb. This is a good idea for all BMW carb models. It stops a lot of problems.

My Basic was already upgraded to 1000 CC.
My bike makes only 450 kms with 35 L gas. It makes nearly 13 km/L. The problem with my bike, repairman doesn't understand how to fix the problem and I can't dare to touch the carbs with fear of destroying it. Many friends who also tried to help you indicated possible problems and how to solve myself. I will have a look how to do it next month.

To you, upgrading to 1000 CC doesn't solve your problems.
Mine is 1000 CC Siebenrock and it is really thurtsy for gas.

__________________
"where the traveller goes, nobody knows ! "

I put Siebenrock on my engine a few years ago (but I also changed the camshaft and ported the tops).
My experience is that if you drive the Siebenrock-kit as a you would drive a R80 it will give you better mileage then the R80, but not much..

IMHO most mileage problems are caused by the carbs, and if you clean them and change the needle and jet (the jet the needle goes through) every 20-30kkm it should be fine.

All jets should be original:
Main jet 135
Idle jet 45
Jet 2.68

Hi Ali Baba and others,

I've written to Bing carburetor about the subject and they recomended to change needle jets and main jets. Normally you've should done this every 25 K kms they say (or let's say 30-35 K kms). Mine is already 44 K kms and sure it is needed to change.

I am going to make additional change of float and bowl kit which are alcohol resistant.
Total cost seems like 300 USD.

I've spoken the main and the best BMW service center named Borusan in Istanbul and they said we don't have enough knowledge to solve your high fuel consumption problem (low mileage). So I decided to solve problem myself. Hope FrankWarner and GS Workshop reads this thread as they too tried to help me a lot with you about this problem.

For info:
www. bingcarburetor.com
e-mail: bingcarburetor@bingcarburetor.com

(I was speaking to Fay)

__________________
"where the traveller goes, nobody knows ! "

Have you solved your problem ?

My R100RT ran on 5.7L/100km at 90km/h which was fine since I am used to 6.5L/100km or there about... on my R80/7RT (rebuilt/overhauled/modified).

My Siebenrock kit (barrels, pistons and heads) have been using anything from 9L to 5.9L/100km at 90km/h constant speed... it is settling down now and seems to be stabilizing around 6.2L/100km at 90km/h.

As for jettings:
BING Power Systems GmbH · Nürnberg
BING POWER SYSTEMS GmbH
click on Service, then on Tuning Manuals
BING POWER SYSTEMS GmbH - Tuning manuals
You will need to fine-adjust the jetting depending on if you move the carbs from the original bike/cc-volume.
I really like the Bing 40mm on 800cc; much smoother running though the down-side is a huge loss in accelleration speed. Top-speed same or just a tiny bit better. Mileage is a tiny bit better. So the trade-off was ok for me.

__________________
Drive Safely,
Albert

I believe the most efficient 'airhead' BMW's were the higher compression (9.2 to 1 as opposed to 8.2 to 1) R75 and R80 models of the late 70's and early 80's ~ 4.5-4.75 liters per 100km. So if fuel economy is the top concern, that would be the setup to have.

I still think that if you are going to convert to 1000cc's the best way to do it is with the complete cylinder/ piston/ heads/ carbs/ exhaust from a stock BMW engine. Fortunately, this is easy to do and pretty much a straight swap with only new gaskets needed. Doing it this way gives you a base line for tuning that you can then stray from if you choose.

Following up on your intermittent loss of power at sustained speeds of 80km/h. I'm on a road trip in Turkey right now having the same problem. Just to clarify, you fixed this problem by cleaning the carbs (again) or sorting the inition issue.

Could be either with me. The crankcase breather sometimes pours oil down the air intake like to the carbs, but I've also recently put on a large 43L tank that may have effected the CDI mounted underneath it.

Thanks for any help you can provide. M.

unfortunately the bike was stolen and crashed so i never got to fix the problem. if you have oil leaking intp the carbs i would try that first though.